Selective breeding and artificial selectionSpec 18.3.2, 18.3.3, 18.3.6
Selective breeding (artificial selection) is when humans choose which organisms breed so that the next generation has desirable features.
- Humans select individuals with desirable features.
- These individuals are crossed (bred together) to produce the next generation.
- Offspring showing the desirable features are selected, and the process is repeated.
This is repeated over many generations. Each generation has more of the desirable features. It is used to improve crop plants and domesticated animals.
| Organism | Desirable features that may be selected |
|---|---|
| Crop plants (wheat, rice) | higher yield, disease resistance, larger seeds or fruits, shorter stems |
| Dairy cattle | high milk yield |
| Beef cattle | large muscle mass, fast growth |
| Hens | large numbers of eggs, large eggs |
Percentage increase in milk yield
A herd of cows had a mean milk yield of 4000 dm³ per year. After many generations of selective breeding the mean yield is 5200 dm³ per year. Calculate the percentage increase.
- Increase = 5200 − 4000 = 1200 dm³
- Percentage increase = (increase ÷ original) × 100 = (1200 ÷ 4000) × 100
Answer: 30%
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanNatural and artificial selection compared
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean| Natural selection | Artificial selection | |
|---|---|---|
| What selects | the environment | humans |
| Features selected | those that help survival and reproduction | those that humans want |
| Purpose | organisms become better adapted to their environment | to improve crops and domesticated animals for human use |
| Speed | usually slow: takes a very long time | usually faster, because humans choose every breeding pair in each generation |
In selective breeding questions state what is selected, that the selected individuals are crossed, that offspring with the feature are chosen, and that it is repeated over many generations.
Quick check
Give two things organisms compete for.
Show answer
Any two from food, water, light, space, mates.
What happens to the alleles of better-adapted individuals?
Show answer
They are passed on to the next generation.
Name the three stages of selective breeding.
Show answer
Select individuals with desirable features; cross them; select offspring showing the desirable features.
Supplement Define adaptation.
Show answer
The process, resulting from natural selection, by which populations become more suited to their environment over many generations.
Supplement Who or what selects in natural selection and in artificial selection?
Show answer
The environment selects in natural selection; humans select in artificial selection.